1. Field of the Invention
The present invention pertains generally to manufacturing devices with nanometer scaled features and more specifically to manufacturing components for a Polarization Beam Splitter (PBS).
2. Description of the Related Art
PBSs have been created having a multilayer polarization splitting elements. The multilayer polarization splitting elements are composed of layers having a high refractive index alternating with layers having a low refractive index. These multilayer polarization splitting elements are constructed using TiO2. Such a PBS is described in U.S. application Ser. No. 11/122,153 entitled “POLARIZATION ELEMENT AND OPTICAL DEVICE USING POLARIZATION ELEMENT” filed May 3, 2005. which issued Dec. 26, 2006 as U.S. Pat. No. 7,155,073.
FIG. 1 is a structural view showing a PBS. FIG. 1 shows a state in which a polarization splitting layer 23 composed of a plurality of periodic structures each having structural birefringence is sandwiched by two prisms. The polarization splitting layer 23 and the two prisms compose an optical element having a polarization splitting function.
In FIG. 1, the polarization splitting layer 23 is tilted at Brewster angle relative to an incident surface 25 of the prism. When an incident light beam including a P-polarized light component 18 and an S-polarized light component 20 is perpendicularly made incident on the incident surface 25, the P-polarized light component 18 passes through the polarization splitting layer 23 to become passing light 19, and the S-polarized light component 20 is reflected on the polarization splitting layer 23 to become reflective light 21. As illustrated herein, the optical element is assumed to be used for visible light.
FIG. 2 is a conceptual view showing the polarization splitting layer 23. The polarization splitting layer 23 has a plurality of grating structures (periodic structures) stacked therein. Periodic directions of adjacent grating structures are substantially orthogonal to each other. In this embodiment, five one-dimensional grating structures corresponding to five layers are stacked. (FIG. 2 is the conceptual view so only three one-dimensional grating structures are shown therein.) Assume that first, second, third, fourth, and fifth one-dimensional gratings are arranged in order from a light incident side (upper side of FIG. 2). A period of each of the grating structures is shorter than a wavelength of any incident light. Each of the grating structures exhibits structural birefringence.
As shown in FIG. 2, an incident surface on which the incident light beam (P-polarized light component 18 and S-polarized light component 20) is made incident is orthogonal to a periodic direction of the first one-dimensional grating. The periodic direction of the first one-dimensional grating is assumed to be a grating direction V. As shown in FIG. 2, a periodic direction of the second one-dimensional grating is orthogonal to the grating direction V and assumed to be a grating direction P.
When the light is made incident on the polarization splitting layer 23, the S-polarized light component is reflected thereon and the reflective light 21 thereof exits from an exit surface 26 different from the incident surface 25 located on the light incident side of the prism. At this time, the P-polarized light component passes through the polarization splitting layer 23 and the passing light 19 thereof exits from an exit surface 27 located on the light exit side of the prism.
This PBS performs well as it has a performance such as wide incident angle as well as broad wavelength. But, it is difficult to make such a device. One difficulty is lies in the stresses that must be applied to the PBS during manufacturing. As the ratio of the height of the grating elements to the width of the grating elements is high, the grating elements may not tolerate lateral stresses induced when the grating structures are stacked or when additional optical elements are bonded to the stack of gratings. In addition, once the PBS is constructed, the PBS may be fragile as shocks experienced by the PBS may be transmitted to the active portions of the stacked gratings which may cause toppling of the grating elements. Finally, as traditional manufacturing processes for the stacked periodic structures leave the periodic structures tightly bound, expansion and contraction of the structures because of temperature changes may cause the shape of the periodic structures to change.
Therefore, a need exists for a manufacturing process that provides for reduced physical and thermal stresses being transmitted to the grating structures in a PBS. Various aspects and embodiments of the present invention meet such a need.